The exact role of Ca ions in regulation of contraction and relaxation of vascular smooth muscle has not yet been determined because of the lack of proper biochemical data. Although the role of Ca ions in such regulation of skeletal and cardiac muscle has been more definitely described and hypothesis as to the mechanism do exist, it may or may not be proper to extrapolate to smooth muscle. This project proposes to isolate and characterize three major membrane components of arterial smooth muscle; sarcoplasmic reticulum Na ion, K ion-ATPase (sarcolemma transport ATPase) and mitochondria. These subcellular organelles will be examined especially with respect to their Ca ions sequestering abilities and ATPase activities, in order to try and assess their particular roles in excitation contraction-coupling in vivo to clarify the mechanism. The effects of c-AMP and protein kinase phosphorylation on the organelles will also be studied with respect to possible control mechanisms. Such studies may lend themselves to detect biochemical alterations which may exist in hypertensive vessels and which may be responsible for increased myogenic tone.